The Stop River is a low and marshy stream in Medfield, Massachusetts, and partly forming the border between Norfolk and Walpole. The river rises near Highland Lake in Norfolk, flows 9.3 miles (15.0 km)^[1] northwards to join the Charles River in Medfield, and ultimately drains into Boston Harbor.

Stop River
Stop River and environs
Physical characteristics
Source
• location	Highland Lake, Norfolk, MA
• coordinates	42°07′35″N 71°18′20″W / 42.12639°N 71.30556°W / 42.12639; -71.30556
Mouth
• location	Charles River, Medfield, MA
• coordinates	42°10′25.2″N 71°19′08.4″W / 42.173667°N 71.319000°W / 42.173667; -71.319000
Length	9.3 miles (15.0 km)

The Medfield Rhododendrons reservation, operated by The Trustees of Reservations, is an important and rare stand of Rhododendron maximum along the river in Woodridge Street, Medfield.